WO2024205971A1

WO2024205971A1 - Rotor assembly for mitigating effects of edgewise flight inflow and methods therefor

Info

Publication number: WO2024205971A1
Application number: PCT/US2024/020426
Authority: WO
Inventors: Bryan Marshall
Original assignee: Supernal LLC
Current assignee: Supernal LLC
Priority date: 2023-03-30
Filing date: 2024-03-18
Publication date: 2024-10-03
Anticipated expiration: 2025-09-30

Abstract

A rotor assembly may include a first rotor mounted on a first drive shaft, and a second rotor mounted on a second drive shaft. The second drive shaft may be concentrically mounted on the first drive shaft. The rotor assembly may include a first motor operatively connected to the first rotor, and a second motor operatively connected to the second rotor. In one example, the first motor may be configured to rotate the first rotor in a first direction, and the second motor may be configured to rotate the second rotor in a second direction. Additionally the rotor assembly may include a controller configured to operate the first and second motors independently to control a blade crossing azimuth based on an angle of inflow.

Description

ROTOR ASSEMBLY FOR MITIGATING EFFECTS OF EDGEWISE FLIGHT INFLOW AND METHODS THEREFOR

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63/493,206 filed March 30, 2023, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to rotor systems for vertical takeoff and landing vehicles. In particular, the present disclosure relates to multi-rotor assemblies that are incorporated in vertical takeoff and landing vehicles and operate during take-off, landing, and transitions to and from cruising modes of vehicle flight.

BACKGROUND

[0003] In contemporary urban environments, the escalating challenges of environmental pollution and traffic congestion have spurred interest in alternative transportation solutions. As urban populations burgeon, the reliance on traditional automobiles and/or public transit for routine activities has become increasingly unsustainable. Accordingly, as a result of the foregoing, there is a growing interest in utilizing aircraft as an alternative means of transportation traditionally undertaken by automobiles. In implementing the strategies for air mobility, challenges exists in ensuring safe vertical takeoff and landing, as well as reducing noise and vibration during edgewise flight. [0004] The present disclosure is accordingly directed to a novel rotor assembly for a vehicle that is configured to mitigate oscillatory forces during edgewise flight, which not only enhances the safety and efficiency of vehicles during critical flight phases but also presents a significant advancement in the search for sustainable and practical air mobility solutions. The background description provided herein is for the purpose of generally presenting the context of the disclosure. Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art, or suggestions of the prior art, by inclusion in this section.

SUMMARY OF THE DISCLOSURE

[0005] Examples described herein include devices, systems, and methods for mitigating the effects of inflow on an AMV as may be experienced by and transmitted from rotors of the AMV. In one example, a rotor assembly may include a first rotor mounted on a first drive shaft, and a second rotor mounted on a second drive shaft. The second drive shaft may be concentrically mounted on the first drive shaft. The rotor assembly may include a first motor operatively connected to the first rotor, and a second motor operatively connected to the second rotor. In one example, the first motor may be configured to rotate the first rotor in a first direction, and the second motor may be configured to rotate the second rotor in a second direction. Additionally the rotor assembly may include a controller configured to operate the first and second motors independently to control a blade crossing azimuth based on an angle of inflow.

[0006] Various aspects of exemplary rotor assemblies according to the present disclosure may include one or more of the following features: each of a first rotor and a second rotor including a two-bladed rotor; a first sensor configured to detect a position of a first rotor, and a second sensor configured to detect a position of a second rotor; a first sensor configured to detect a speed of the first motor and a second sensor configured to detect a speed of a second motor; and a first bearing and a second bearing located concentrically between a first drive shaft and a second drive shaft.

[0007] Various additional aspects of exemplary rotor assemblies according to the present disclosure may include one or more of the following features: a second motor positioned along a longitudinal axis of the rotor assembly between a first bearing and a second bearing; a hub of a first rotor mounted to a distal end of a first drive shaft relative to an engagement between the first drive shaft and the bearing; a hub of a second rotor mounted to a distal end of a second drive shaft relative to an engagement between a second drive shaft and a bearing; a first motor attached to a first drive shaft between the first rotor and a second rotor along a longitudinal axis of the rotor assembly; and a second motor attached to a second drive shaft between a first rotor and a second rotor along a longitudinal axis of the rotor assembly.

[0008] In another example, an exemplary air mobility vehicle (“AMV”) according to the present disclosure may include a fuselage, first and second wings attached to the fuselage, first and second rotor assemblies attached to the first wing, and third and fourth rotor assemblies attached to the second wing. In one example, the AMV may include at least one lift rotor assembly attached to the first wing, and a controller configured to operate the at least one lift rotor assembly. In some examples, the at least one lift rotor assembly may include a first rotor mounted on a first drive shaft, a second rotor mounted on a second drive shaft concentrically mounted on the first drive shaft, and a bearing disposed between the first drive shaft and the second drive shaft. The at least one lift rotor assembly may further include: a first motor operatively connected to the first rotor and configured to rotate the first rotor in a first direction; and a second motor operatively connected to the second rotor and configured to rotate the second rotor in a second direction. According to various aspects of the present disclosure, the controller may operate the first motor and the second motor of the at least one lift rotor assembly independently to control a respective blade crossing azimuth.

[0009] Various aspects of exemplary rotor assemblies relating to AMVs according to the present disclosure may include one or more of the following features: each of a first rotor and a second rotor of a rotor assembly including a two- bladed rotor; at least one lift rotor assembly of an AMV including first and second lift rotor assemblies such that a controller operates first and second motors for the first lift rotor assembly independently of first and second motors of the second lift rotor assembly to independently control a blade crossing azimuth for each of the first and second lift rotor assemblies; a controller configured to operate first and second motors for a first lift rotor assembly to provide a first blade crossing azimuth that is normal to an angle of a respective inflow for the first lift rotor assembly, and operate first and second motors for a second lift rotor assembly to provide a second blade crossing azimuth that is normal to an angle of respective inflow for the second lift rotor assembly.

[0010] Various additional aspects of exemplary rotor assemblies relating to AMVs according to the present disclosure may include one or more of the following features: at least one lift rotor assembly including a first sensor configured to detect a position of a respective first rotor, and a second sensor configured to detect a position of a respective second rotor; and a first sensor configured to detect a speed of a respective first motor, and a second sensor configured to detect a speed of a respective second motor.

[0011] In still another example according to the present disclosure, a method of controlling a blade-crossing azimuth for rotors of a counter-rotating multi-rotor assembly may include receiving system monitored parameter information and determining inflow parameter values, and determining a required blade crossing azimuth based on the inflow parameter values. The method may further include accessing rotor speeds for the rotors and determining an operational blade crossing azimuth, and determining a speed deviation for each of the rotors based on an azimuth deviation between the required blade crossing azimuth and the operational blade crossing azimuth. According to another example, the method may include controlling a motor for each of the rotors based on a respective speed deviation.

[0012] Various additional aspects of exemplary methods according to the present disclosure of controlling a blade-crossing azimuth for rotors of a counterrotating rotor assembly may include: monitoring rotors for realization of a required blade crossing azimuth, and determining an absolute speed deviation between rotor speeds; and logging values of operating parameters at a time of realization including an amount of time between a determination of a required blade crossing azimuth and the realization.

[0013] The examples summarized above can each be incorporated into a non- transitory, computer-readable medium having instructions that, when executed by a processor associated with a computing device, causes the processor to perform the stages described. Additionally, the example methods summarized above can each be implemented in a system including, for example, a memory storage and a computing device having a processor that executes instructions to carry out the stages described.

[0014] The foregoing is a summary and thus may contain simplifications, generalizations, and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting.

[0015] For a better understanding of the embodiments, together with other and further features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying drawings. The scope of the invention will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the disclosed embodiments, and together with the description, serve to explain the principles of the disclosed embodiments. There are many aspects and embodiments described herein. Those of ordinary skill in the art will readily recognize that the features of a particular aspect or embodiment may be used in conjunction with the features of any or all of the other aspects or embodiments described in this disclosure. In the drawings:

[0017] FIG. 1 depicts a perspective view of an exemplary vehicle with vertical takeoff and landing capabilities, according to one or more embodiments of the present disclosure.

[0018] FIG. 2 depicts an exemplary coaxial multi-rotor assembly, according to one or more embodiments of the present disclosure. [0019] FIG. 3 depicts a flowchart of an example method for optimizing counter rotation of rotors in coaxial multi-rotor assemblies, according to one or more embodiments of the present disclosure.

[0020] FIGS. 4A-4D depict operational states of a coaxial multi-rotor assembly under different inflow conditions, according to one or more embodiments of the present disclosure.

[0021] FIG. 5 depicts an exemplary system for optimizing rotations of multiple coaxial multi-rotor assemblies incorporated in an exemplary vertical takeoff and landing vehicle, according to one or more embodiments of the present disclosure.

[0022] FIGS. 6-8 depict operational states of an exemplary vehicle and multiple coaxial multi-rotor assemblies for the vehicle under different inflow conditions, according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0023] The terminology used below may be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific examples of the present disclosure. Indeed, certain terms may even be emphasized below; however, any terminology intended to be interpreted in any restricted manner will be overtly and specifically defined as such in this Detailed Description section.

[0024] In this disclosure, the term “based on” means “based at least in part on.” The singular forms “a,” “an,” and “the” include plural referents unless the context dictates otherwise. The term “exemplary” is used in the sense of “example” rather than “ideal.” The terms “comprises,” “comprising,” “includes,” “including,” or other variations thereof, are intended to cover a non-exclusive inclusion such that a process, method, or product that comprises a list of elements does not necessarily include only those elements, but may include other elements not expressly listed or inherent to such a process, method, article, or apparatus. Relative terms, such as “about,” “approximately,” “substantially,” and “generally,” are used to indicate a possible variation of ±10% of a stated or understood value. In addition, the term “between” used in describing ranges of values is intended to include the minimum and maximum values described herein. The use of the term “or” in the claims and specification is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” As used herein “another” may mean at least a second or more.

[0025] As used herein, the term “vehicle” may refer to various types of aerial vehicles (e.g., planes, helicopters, etc.). Various embodiments of the present disclosure relate generally to electric vehicles, such as vehicles driven via one or more electric loads, components associated with the electrical loads, and monitoring systems for the electrical loads and/or the components associated with the electrical loads. The electric loads may be in the form of electric motors associated with one or more propellers of a vertical takeoff and landing vehicle. Various embodiments of the present disclosure may relate generally to a hybrid class of aircraft that utilizes hydrogen fuel cells or other energy storage/conversion systems for providing electricity to power electric motors.

[0026] Various embodiments of the present disclosure relate generally to electric vehicles, such as vehicles driven via one or more electric loads, components associated with the electrical loads, and monitoring systems for the electrical loads and/or the components associated with the electrical loads. The electric loads may be in the form of electric motors associated with one or more propellers of an electric vertical takeoff and landing vehicle (eVTOL).

[0027] Various embodiments of the present disclosure relate generally to multi-rotor assemblies that may include coaxial rotors that are independently driven and subject to independent hub moment reaction forces. Counter rotation of exemplary coaxial rotor assemblies of the present disclosure may be phase- optimized by operation of independent drives with exemplary systems according to exemplary methods described herein.

[0028] Due to environmental pollution and traffic congestion in urban areas, there is growing interest in alternatives to using automobiles or public road transit to accomplish daily and otherwise routine activities. Air mobility, generally recognized as the use of aircrafts for daily commute activities traditionally accomplished using an automobile, has been highlighted as a potentially effective means of transportation to resolve traffic congestion and reduce environmental pollution in various areas where automobile use is very high, such as in cities.

[0029] One objective that has been identified for this mode of transportation is an ability to have an individual or a group of people be able to board an air mobility vehicle (“AMV”), and have that vehicle take off and land, in urban areas. A key component to delivering this capability is equipping AMVs with technology, both mechanical and system control-based, that enables safe vertical takeoff and landing. Another significant design consideration includes minimizing noise and vibration, particularly resulting from rotor operation.

[0030] Some AMVs may include a fuselage, one or more wings, and two types of rotors - lifting rotors and propulsion rotors. Propulsion rotors in some AMVs may be provided by tilting rotors. However, regardless of whether propulsion rotors are configured to tilt, the lifting rotors are primarily responsible for generating lift forces for taking off and landing an AMV. In addition to takeoff and landing, lifting rotors for an AMV may be required to operate during an edgewise flight mode of operation. Edgewise flight for an AMV may include translational movement of the AMV that is not part of taking off or landing. Flight assistive operation of lifting rotors may be required from a time when an AMV transitions from a takeoff operation mode (e.g., hovering) into edgewise flight, until the AMV reaches a minimum speed in a direction of the edgewise flight. Once that minimum speed is reached, lifting rotors may be stopped and aligned with the direction of flight to minimize their drag.

[0031] While lifting rotors can assist an AMV in edgewise flight, different types of blade configurations for lifting rotors present different issues and advantages that may dictate, to varying degrees, other design requirements for the AMV. In turn, various constraints for achieving or meeting these requirements - cost, overall weight, part availability, part compatibility, overall complexity - may ultimately decide which blade configuration is utilized for the lifting rotors. For example, two-bladed rotors exhibit lower drag than rotors with more than two blades when they are stopped. Also, two-bladed rotors may weigh less than three-bladed rotors, for example, and thus may make it easier for an AMV to reach a speed at and above which assistance from the lifting rotors is no longer needed. On the other hand, two- bladed rotors may have the potential to generate large vibrations in certain situations if complex mitigations are not implemented.

[0032] Oscillatory forces resulting from a lift disparity between advancing and retreating blades may be generated by rotor assemblies during edgewise flight. This includes counter rotating coaxial lift rotor assemblies that may be incorporated in some AMVs. At least with respect to these AMVs, the oscillatory forces can result in the generation of vibrations in the motors driving the rotors and in the structures of the AMVs surrounding those motors (e.g., airframe for the AMVs). Oscillatory forces resulting from a lift disparity between advancing and retreating blades during edgewise flight may be minimized by applying cyclic pitch change and/or employing more than two rotor blades per rotor.

[0033] To effect cyclic pitch change of rotor blades, a rotor assembly, may be equipped with a swash plate. Generally, a swash plate may translate a motion from a pilot and turn it into a motion of rotor blades so that at the same time: (1 ) an advancing blade angle of attack can be reduced, and (2) an angle of attack of a retreating blade can be increased to balance out the lift generated by the advancing blade.

[0034] A typical swash plate may include an entraining disc that may be controlled by three actuating devices to change the pitch of rotor blades collectively and/or cyclically. During operation, a swash plate may: (1 ) decrease and increase blade angles of attack to match a flow of air so that a rotor makes a consistent thrust all the way around a circumference of the disc such that a helicopter may go up or down; and (2) change blade angle of attack cyclically to aerodynamically tilt the rotor disc and maneuver a vertical takeoff and landing vehicle, such as a helicopter. Different mechanisms and systems, such as pneumatic, electric or hydraulic systems, may be used to change the angles of these swash plates. In addition, each swash plate may employ multiple actuators.

[0035] Swashplates are effective for changing rotor blade pitch angles and enabling rotor blade operations that are central to core functionalities (e.g., moving up and down and maneuvering during flight) of a vertical takeoff and landing vehicle.

However, despite their effectiveness, incorporating swashplates in lifting rotors for AMVs adds significant weight, complexity, and cost, each of which alone is likely to render AMV development, construction, and operation unmanageable, unable to be scaled, and/or unattractive from a business point of view.

[0036] In view of the foregoing issues, a need exists for devices, systems, and methods that provide rotor assemblies that mitigate the effects of inflow on lifting rotors, particularly when the lifting rotors are operated during edgewise flight. More particularly, by properly phasing a pair of rotors rotating in opposite directions on concentric drive shafts and coupling the drive shafts in such a way as to share bending loads, but not rotational torque or speed, oscillatory forces generated in edgewise flight can largely be eliminated. As configured, the rotors may resolve equal and opposite oscillatory hub moments within a drive shaft assembly and prevent these loads from passing through independently driven rotor motors and being transmitted to surrounding components and structures, such as a vehicle airframe. Active azimuth phase adjustments of the two rotors according to embodiments of the present disclosure maintain vibration cancellation in all azimuths of flight relative to an orientation of inflow to a rotor assembly including the two counter rotating rotors.

[0037] Reference will now be made in detail to the exemplary embodiments of the present disclosure described below and illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts.

[0038] Additional objects and advantages of the embodiments will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the embodiments. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claims.

[0039] Referring now to FIG. 1 , a perspective view of an exemplary vehicle with vertical takeoff and landing capabilities is depicted, according to one or more embodiments.

[0040] An exemplary AMV 100 according to the present disclosure may include a fuselage 170 having a boarding space and a boarding gate, first and second wings 140, 145 disposed on fuselage 170, rotor assemblies 160, 162, and lifting rotor assemblies 105-1 to 105-4 (referred to hereafter as “lifting rotor assemblies 105-1 to 105-4” or “lifting rotor assemblies 105” unless referring to specific individual or sub-groups of these lifting rotor assemblies). In one embodiment, AMV 100 may be, for example, a distributed electric propulsion (DEP) electric vertical takeoff and landing vehicle that employs electric power via, e.g., an onboard battery system. In addition, each of tilting rotor assemblies 160, 162, and each rotor 110, 130 of each lifting rotor assembly 105, may be driven by a single or a plurality of electric motors. As shown in FIG. 1 , AMV 100 may be equipped with batteries 180 for supplying electrical energy to the one or more electric motors. The batteries may be disposed in a lower part of fuselage 170 and/or beneath passenger seats and within fuselage 170, and/or in an extension part that extends rearward from fuselage 170 to second wing 145.

[0041] As shown, first wing 140 (main wing) is longer than second wing 145 (tail wing). Two tilting rotor assemblies 160 disposed on first wing 140, as well as first and third lifting rotor assemblies 105-1 , 105-3 may be disposed to be horizontally aligned. Second and fourth lifting rotor assemblies 105-2, 105-4 may be disposed at a rear of main wing 140, and two tilting rotors 162 may be disposed at second wing 145. Second lifting rotor 105-2 may be horizontally aligned with fourth lifting rotor assembly 105-4, and tilting rotors 162 may also be in horizontal alignment between the fuselage 170 and the second and fourth lifting rotor assemblies 105-2, 105-4. Through this disposition structure, a balance control may be possible during both lifting and cruising.

[0042] In one embodiment, a boarding gate (not shown) may be disposed on a side of fuselage 170 rather than on a front or rear of it. This configuration may enable passengers to easily embark and disembark during boarding. Additionally or alternatively, this configuration may provide a safe passage space through lower spaces of tilting 160, 162 and lifting rotor assemblies 105, which are disposed in close proximity to fuselage 170. More specifically, first tilting rotors 160 may be installed on first wing 140 (main wing) away from fuselage 170 as much as possible. This may enable passengers to conveniently reach the boarding gate. Furthermore, relative to a configuration in which tilting rotors are disposed close or proximate to fuselage 170, the exemplary configuration in FIG. 1 may generate less continuous noise and/or vibration during cruising, thereby improving the ride quality.

[0043] In one embodiment, propellers 168 of tilting rotor assemblies 160, 162 may be mounted on respective first booms 166. As shown in FIG. 1 , propellers 168 may be five-bladed propellers to provide sufficient propulsion force during cruising. However, those of ordinary skill in the art will readily understand that a greater or lesser number of blades is within the scope of this disclosure. In addition to components for rotating propellers 168, each of tilting rotor assemblies 160, 162 may be respectively provided with a separate actuator for rotor tilting. In one embodiment, when one of tilting rotor assemblies 160, 162 is tilted upward, the tilting rotor may be about level (parallel) to the ground as shown in FIG. 1. In this position, tilting rotor assemblies 160, 162 may be operated to perform a lifting function together with lifting rotor assemblies 105. However, when capacity or power of tilting rotor assemblies 160, 162 is increased for lifting, excessive noise and/or vibration caused by tilting rotor assemblies 160, 162 may occur during cruising thereafter. As a result, AMV 100 may be configured, during lifting and cruising operations, to reduce capacity and power of tilting rotor assemblies 160, 162 to the maximum extent possible. Accordingly, lifting rotor assemblies 105 may be provided separately to primarily handle the generation of sufficient lift when taking off and landing.

[0044] As shown in FIG. 1 , in one embodiment, AMV 100 may incorporate four lifting rotor assemblies 105 - at least two lifting rotor assemblies 105-1 , 105-2 disposed on a first side (e.g., left side in FIG. 1 ) of fuselage 170 and two lifting rotor assemblies 105-3, 105-4 disposed on a second side (e.g., right side in FIG. 1) of fuselage 170. Even numbers of lifting rotor assemblies may provide advantages in terms of balance control, but one of ordinary skill in the art will recognize that an AMV, such as AMV 100, may be provided with an odd number of lifting rotor assemblies. Indeed, even though four lifting rotor assemblies 105-X are depicted in FIG. 1 , such a configuration is not limiting and persons skilled in the art may realize that AMV 100 may include any suitable number of lifting rotor assemblies 105-X. For example, AMV 100 may contain three lifting rotor assemblies 105-X, two disposed on a first side of fuselage 170 and one disposed on a second side of fuselage 170. In addition to the operational schemes described above (lifting rotor operation during, e.g., takeoff, landing, and transitions), when any one of tilting rotor assemblies 160,

162 and lifting rotor assemblies 105 fails, the titling and lift rotor assemblies that remain operational may perform balance control. Therefore, when lifting is necessary, such as during hovering or in a transition stage of flight when flight is edgewise, sufficient lift is provided to allow for the balance control of fuselage 170 and control in an emergency situation.

[0045] On the other hand, when tilting rotor assemblies 160, 162 are tilted downward from a horizontal state shown in FIG. 1 , tilting rotor assemblies 160, 162 may adjust to face towards a front of fuselage 170. In this position, tilting rotor assemblies 160, 162 may generate propulsion force during flying or cruising of fuselage 170. During the flight of AMV 100, fuselage 170 may be configured to generate lift using tilting rotor assemblies 160, 162, and, as necessary, tilting rotor assemblies 160, 162 may also be operated together with lifting rotor assemblies 105 to reinforce lift. Such a combined operation of tilting 106, 162, and lifting rotor assemblies 105, may be implemented in edgewise flight of AMV 100 where fuselage 170 is not moving fast enough after takeoff and before landing to generate sufficient lift, e.g., via wing 140.

[0046] Lifting rotor assemblies 105 may be necessary to provide lift during vertical takeoff and landing of fuselage 170. Additionally, operation of lifting rotor assemblies 105 may be needed to assist tilting rotors 160, 162 in the propulsion of fuselage 170 during flight transitions from taking off until reaching certain speeds. More specifically, a transition may encompass a portion of edgewise flight by AMV 100 after takeoff but before AMV 100 reaches a predetermined speed (e.g., a cruising speed) at which first and second wings 140, 145 provide the lift required for continued flight operation of AMV 100 absent assistance from lifting rotor assemblies 105. For instance, in one example, AMV 100 may need to be traveling at a speed of approximately 70 miles per hour before operation of lifting rotor assemblies 105 can be stopped. [0047] In an embodiment, individual rotors of lifting rotor assemblies 105 may be configured with two blades that may be sized based on a criteria of maximally reducing flight resistance when the rotor is not in operation. In other embodiments, different numbers of blades may be incorporated in the rotors depending on various constraints and/or new capabilities such as inflow, flight resistance, weight, and/or motor speed and/or torque. In addition, upon reaching a minimum speed marking an end to a transition phase of flight, lifting rotors assemblies 105 may be stopped in a specific position relative to respective booms 106 to minimize any flight resistance lifting rotor assemblies 105 may create when not operating. For instance, as shown in FIG. 1 , first and second rotors 110, 130 of lifting rotor assemblies 105 may be double-bladed rotors, and may be stopped in alignment with respective booms 106 to maximally reduce the flight resistance during cruising.

[0048] Also shown FIG. 1 is a single first rotor 110 for each rotor assembly 105 positioned below a respective boom 106, and a single second rotor 130 for each rotor assembly 105 positioned above a respective boom 106. However, exemplary rotor assemblies described herein are not limited to the configuration depicted in FIG. 1 with respect to: total number of rotors; number of rotors above and below a boom; inclusion of a boom; or location of a boom, if incorporated, relative rotor assembly rotors. Rather, exemplary rotor assemblies according to the present disclosure may include stacked rotors, each driven independently by a respective motor. In some examples, a rotor assembly may include a stack of at least two rotors positioned above a boom, each rotor in the stack being driven by a respective motor independently of motors of other rotors. In other examples, a rotor assembly may include more than two rotors, a first motor that drives a group of rotors having more than one rotor, and at least a second motor that drives, independently of the first motor, at least one other rotor of the rotor assembly not included in the group of rotors.

[0049] As discussed above, while at cruising speed, stopping lifting rotor assemblies 105 from operation may effectively reduce flight resistance. Furthermore, when lifting rotor assemblies 105 are stopped from operation, fuel efficiency may be improved by controlling a resting position of propellers 110, 130 so that they are aligned in parallel to the direction in which the fuselage is flying, thereby maximally reducing flight resistance. In addition to these advantages, exemplary rotor assemblies described herein (e.g., such as the lifting rotor assemblies 105 for AMV 100) may be counter-rotating rotors configured and controlled to minimize operational vibrations typically generated by rotors during edgewise flight as a result of a varying inflow angle.

[0050] More specifically, each of lifting rotor assemblies 105 for AMV 100 may be a coaxial counter- rotating multi-rotor assembly including rotors that are azimuthally phased such that the rotors are at maximum flap locations normal to an inflow angle at a same instant in time, and thereby creating equal and opposite hub moments. These forces counter each other leaving the net oscillatory hub moment near to zero. Furthermore, as described in more detail below, blade passage of rotors, such as first and second rotors 110, 130 of lifting rotor assemblies 105 of AMV 100, may be actively managed during operation by exemplary controllers according to the present disclosure. Small variations in revolutions per minute (rpm) of one or both drive motors may be used to change the azimuth of the blade passage. [0051] As used herein, an azimuth may correspond to an angular measurement in a spherical coordinate system, and more specifically, a horizontal angle from a cardinal direction, such as north.

[0052] FIG. 2 depicts an exemplary coaxial multi-rotor assembly 205 (“rotor assembly 205”), according to one or more embodiments. As depicted, rotor assembly 205 includes first and second drive shafts 214, 234 that are extended and joined to each other by a pair of concentric bearings - first and second bearings 216, 236. The first and second bearings 216, 236 enable first and second motors 212, 232 to respectively operate and drive first and second rotors 210, 230 at disparate rotational velocities and in different directions. At the same time, opposing oscillatory hub moments may be transmitted through first and second drive shafts 214, 234 and first and second bearings 216, 236, without imparting these loads on first and second motors 212, 232 or a surrounding structure 240, which may include an airframe structure for an AMV.

[0053] During operation, first rotor 210 may rotate in a first direction 215 and second rotor 230 may counter- rotate in a second direction 235 opposite to the first direction 215. As a blade of second rotor 230 moves in second direction 235, advancing blade 230A may rotate into oncoming airstream and create lift as retreating blade 230B moves away from that oncoming airstream generating less lift (or even drag) as a result of relative airflow. On the other hand, advancing blade 210A of first rotor 210 will be rotating into an oncoming airstream in first direction 215 opposite to second direction 235 and thereby create lift, while a retreating blade 210B moves away from the oncoming airstream.

[0054] A blade crossing azimuth is an azimuth at which first rotor 210 is in rotational alignment with second rotor 230. As applied to rotor assembly 205, at a blade crossing azimuth, two blades on second rotor 230 pass over the two blades of first rotor 210. Examples of instances of counter-rotating coaxial blades exhibiting a blade crossing azimuth are provided in FIGS. 4B and 4D. In one example, each of first and second rotors 210, 230 may be rotating at a speed in excess of 900 revolutions per minute (RPM), and each may create significantly large forces that may be transmitted to a respective motor and surrounding structure 240. However, as first and second rotors 210, 230 rotate in opposite directions, the forces they generate also act in opposite directions (i.e., vectors of the generated forces oppose one another). Thus, at the instance of the blade crossing azimuth, these significant forces acting in opposite directions may substantially, partially, or completely cancel each other out.

[0055] Due to the substantial, partial, or complete force cancelation described above, neither of the forces generated from either rotor is reacted fully, or at all, into first and second motors 212, 232 or surrounding structure 240. Furthermore, neither of the generated forces may be taken fully, or at all, through a wing of an AMV that may include rotor assembly 205. As a further result, rotor assembly 205, and the other exemplary rotor assemblies described herein, may: (1) cancel a majority of problematic vibrations during edgewise flight, particularly in lifting rotors, without adding the weight and complexity of traditional systems; and (2) cancel those vibrations internal to a drive shaft assembly without passing the vibrations through motors and to a surrounding structure of a vertical takeoff and landing vehicle (e.g., an airframe structure of an AMV).

[0056] As previously noted, first rotor 210 may be operated by first motor 212 independently of an operation of second rotor 230 by second motor 232. Controller 250 may communicate with and control first and second motors 212, 232 based on input from different information sources. In one embodiment, controller 250 may communicate with first and second sensors 218, 238 to monitor and/or determine angular velocities of first and second rotors 210, 230, motor speeds, and/or rotor positions. In one example, first and second sensors 218, 238 may include position sensors, such as hall sensors, and may be utilized to track an azimuth of each individual rotor. In one example, first and second sensors 218, 238 may track positions of respective reference points on first and second rotors 212, 232, based on which the azimuth of each rotor may be determined.

[0057] In still other examples, first and second sensors 218, 238 may include sensors configured to measure forces being generated and/or transmitted through first and second drive shafts 214, 234. One embodiment of this example may include position sensors that measure an axial displacement either of first and second drive shafts 214, 234 and/or first and second bearings 216, 236, and this information may be used to derive forces being applied thereto. In yet still other examples, the first and second sensors 218, 2328 may include sensors configured to measure vibrations or vibratory oscillations of various components, including, for instance, first and second motors 212, 232, first and second drive shafts 214, 234, first and second bearings 216, 236, and/or other components of rotor assembly 205 or an AMV including rotor assembly 205 attached to first and second motors 212, 232 and drive shafts 214, 234.

[0058] In one embodiment, controller 250 may utilize information on a condition of an AMV to control first and second motors 212, 232 to dictate a blade crossing azimuth based on a direction of inflow on rotor assembly 205. More specifically, operating states of different vehicle components, such as elevators, ailerons, rudders, and pitch angles of tilting rotors may be tracked and used to calculate or otherwise derive a direction of the wind the AMV is experiencing.

[0059] FIG. 3 depicts a flowchart of an example method for optimizing counter rotation of rotors in coaxial multi-rotor assemblies, according to one or more embodiments.

[0060] At 310, system monitored parameter information may be received and inflow parameter values, such as magnitude and direction (vector) may be determined.

[0061] At 320, a required blade crossing azimuth may be determined based on the inflow parameter values.

[0062] At 330, current rotor speeds may be detected or otherwise determined, and an operational blade crossing azimuth may be determined and/or registered.

[0063] At 340, speed deviation for each rotor based on an azimuth deviation between a required blade crossing azimuth and the operational blade crossing azimuth may be determined.

[0064] At 350, a motor for each rotor of the coaxial multi-rotor assembly may be operated based on a respective speed deviation. More specifically, the speeds of each motor may be changed to resolve respective speed deviations and for the rotors exhibit the required blade crossing azimuth.

[0065] In some examples, a degree of precision of the control of lift rotor assemblies provided by exemplary methods of the present disclosure, may allow for increased usage of the lift rotor assemblies in assisting the titling rotors assemblies with propulsion, and/or reduced usage of the tilting rotor assemblies in assisting the lift rotor assemblies with lifting operations. As a result of the reduced usage, service life considerations that may impact a sizing and selection of tilt rotor assemblies may be minimized. As a further result, smaller sized tilt rotor assemblies having a similar output (thrust capability) as larger tilt rotor assemblies, but shorter service lives, may be incorporated in an AMV construction. In turn, these smaller tilt rotor assemblies may leave room for larger passage-type spaces.

[0066] At 360, rotors for the coaxial rotor assembly may be monitored to identify when the required blade crossing azimuth is realized. At that point, an absolute speed deviation between rotor speeds may be recognized from the then operational speeds of the motors. In turn, values of operating parameters at the time of realization, including an amount of time between required blade crossing azimuth determination and realization, may be logged in, for example, a memory.

[0067] FIGS. 4A-4D depict operational states of a coaxial multi-rotor assembly 405 under different inflow conditions, according to one or more embodiments.

Because the inflow angle may vary with a direction of flight and a prevailing wind, it is necessary to actively manage a blade passage azimuth during lift rotor operation. Exemplary controllers according to the present disclosure may be configured to make small variations in rpm of one or both drive motors independently driving coaxial rotors to change an azimuth of blade passage. FIGs. 4A-4D illustrate coaxial blade passage azimuths for counter rotating first and second rotors 410, 430 that are normal to a changing inflow at different points in time.

[0068] As shown in FIG. 4A, first rotor 410 is rotating in first direction 415 at a first angular velocity (coi ) as second rotor 430 rotates in second direction 435 opposite to first direction 415 at a second angular velocity (02). As with the first and second rotors 210, 230 depicted in FIG. 2, each of first and second rotors 410, 430 may be independently driven by a respective motor such that an azimuth of first blade crossing 450 is normal to first inflow 400 as shown in FIG. 4B. [0069] A vector of an inflow may, and is likely to, change during edgewise flight. FIG. 4C depicts first rotor 410 rotating in first direction 415 at a third angular velocity (03) as second rotor 430 rotates in second direction 435 opposite to first direction 415 at a fourth angular velocity (04). As a result, an azimuth of second blade crossing 455 may be normal to second inflow 402, as shown in FIG. 4D. More specifically, a controller, such as the exemplary controller 250 of FIG. 2, may determine or otherwise access information corresponding to an angle (direction) of second inflow 402. Based on this angle information, the controller may estimate angular and motor speeds required to yield blades of second rotor 430 crossing over blades of first rotor 410 at an azimuth shown in FIG. 4D which is: (1 ) different from the blade crossing azimuth corresponding to the first inflow 400; and (2) normal to the second inflow 402.

[0070] FIGS. 4A-4D illustrate azimuthally phasing coaxial rotors so that rotors are at their maximum flap locations normal to an inflow angle at a same instant in time, for two different inflow angles at two different times. Relative to FIGS. 4A and 4B, FIGS. 4C and 4D illustrate a blade passage azimuth adjustment following a change to an inflow angle. At each instance depicted in FIG. 4B and FIG. 4D, first and second rotors 410, 430 are at their maximum flap locations normal to a respective inflow angle, such that equal and opposite hub moments are created from these first and second rotors 410, 430. As a result, these forces counter each other and leave a net oscillatory hub moment near zero. Thus, driving first and second rotor 410, 430 independently in an azimuthally phased manner may provide the operational capabilities of a swash plate to the extent that the independently driven motors may entirely substitute for having a swash plate on rotor assembly 405. [0071] FIG. 5 depicts an exemplary system 500 for optimizing rotations of multiple coaxial multi-rotor assemblies incorporated in an exemplary vertical takeoff and landing vehicle, according to one or more embodiments.

[0072] In one embodiment, system 500 may include controller 550 and first, second, third, and fourth coaxial multi-rotor assemblies 505-1 , 505-2, 505-3, 505-4 (“rotor assemblies 505”). Each of rotor assemblies 505 may include a pair of rotors, with each rotor being operated by a respective motor, and each motor controlled by a respective motor controller based on data from a respective speed sensor. In addition, in some embodiments, one or more of the rotor assemblies may include an inflow sensor and/or a coordination controller for a respective pair of rotors. Each coordination controller may serve as part of a distributed control scheme or provide redundancy to controller 550. That is, each coordination controller may independently operate respective motors in such a way as to azimuthally phase rotors rotating in opposite directions on concentric drive shafts coupled in such a way as to share bending loads, but not rotational torque or speed, and thereby substantially eliminate oscillatory forces generated in edgewise flight.

[0073] In one embodiment, controller 550 may include a processor, a communications module, an inflow sensor, and various other sensors that provide data corresponding to a condition of an AMV. In addition, controller 550 may implement azimuth crossing, rotor coordination, and inflow sensing services. Each of the services running or otherwise being implemented by controller 550 can be part of or configured to be compatible with a software product that is at least partially provided by the controller. In one example, the software product can provide tools for system management, communication and coordination, modeling, motor operation, tracking rotor positions, generating components of and supporting selections made through a user interface, and any other relevant features.

[0074] In one embodiment, the azimuth crossing service may determine an azimuth for a blade crossing for each rotor assembly based on an inflow angle detected by an inflow sensor for system 500, or determined by an inflow sensing service for system 500 and/or each rotor assembly 505. In another embodiment, each rotor assembly 505 may include an inflow sensor as noted above, which detects an inflow angle for a respective rotor assembly and communicates that inflow angle to controller 550 via the communications module (“comms mod” in FIG. 5). In still another embodiment, the azimuth crossing service may rely on information from the AMV sensors to determine inflow parameters for each of rotor assemblies 505. The rotor coordination service may be configured to receive outputs from the azimuth crossing service and determine motor speeds and operations required for a respective required blade crossing azimuth to be realized by each rotor assembly. In one embodiment, motor speeds and operations determined by the rotor coordination service may be communicated to motor controllers for the rotor assemblies via the communications module.

[0075] Controller 550 and at least the motor controller of each rotor assembly, may constitute a computing device including a processor, a memory storage, and a non-transitory computer-readable medium containing instructions that are executed by the processor. In addition, the controller 550 and each of rotor assemblies may include one or more sensors installed in the controller or assembly in communication with a respective processor.

[0076] FIGS. 6-8 depict exemplary operational states of AMV 600 and multiple coaxial multi-rotor assemblies for AMV 600 under different inflow conditions, according to one or more embodiments. In one embodiment, AMV 600 may include first, second, third, and fourth coaxial multi-rotor assemblies 605-1 , 605-2, 605-3,

605-4 (“rotor assemblies 605”). Each rotor assembly 605 may include first rotor 610 configured to rotate in first direction 615, and second rotor 630 configured to rotate in second direction 635. In one embodiment, one or both of first and second rotors 610, 630 incorporated in any of the rotor assemblies may be provided by a very simple, one piece composite structure from one blade end to another blade end, with a bore provided in the middle. Thus any of first and second rotors 610, 630 of AMV 600 may be a simple lightweight one-piece composite structure.

[0077] Figure 6 depicts each rotor assembly 605 in a state in which the respective first and second rotors 610, 630 are not crossing. On the other hand, FIG. 7 illustrates an instance in which respective first and second rotors 610, 630 for each rotor assembly 605 cross (as controlled by a controller similar to controller 550 in FIG. 5) at a same blade crossing azimuth 700. In an embodiment, AMV 600 may implement a controller, such as controller 550 of FIG. 5 that may determine that an inflow angle is the same for each of rotor assemblies 605, and as a result sets and operates respective motor rotors to rotate at respective speeds such that each pair of rotors exhibits the same blade crossing azimuth 700. The same blade crossing azimuth 700 being normal to an inflow angle 701 to which each rotor assembly 605 is subject to.

[0078] In still another instance illustrated in FIG. 8, respective first and second rotors 610, 630 for first and second rotor assemblies 605-1 , 605-2 cross (as controlled by a controller similar to controller 550 in FIG. 5) at a first blade crossing azimuth 800. The first blade crossing azimuth 800 being normal to a first inflow angle 801 to which the first and second rotor assemblies 605-1 , 605-2 are subject to. At the same instant, first and second rotors 610, 630 for third and fourth second rotor assemblies 605-3, 605-4 cross at a second blade crossing azimuth 802. The second blade crossing azimuth 802 being normal to a second inflow angle 803 to which the third and fourth rotor assemblies 605-3, 605-4 are subject to.

[0079] An exemplary controller for the AMV 600 may determine that an inflow angle is the same for the first and second rotor assemblies 605, but different from an inflow angle to which the third and fourth rotor assemblies 605-3, 605-4 are experiencing. As a result, the controller may set, and operate respective motor rotors for the first and second rotor assemblies 605-1 , 605-2 to rotate at respective speeds such that each pair of rotors exhibits, the first blade crossing azimuth 800. The first blade crossing azimuth 800 being normal to the inflow angle to which each of first and second rotor assemblies 605-1 , 605-2 is subject to. At the same instant, the controller may set, and operate respective motor rotors for third and fourth rotor assemblies 605-3, 605-4 to rotate at respective speeds such that each pair of rotors exhibits second blade crossing azimuth 850. Second blade crossing azimuth 850 being normal to the inflow angle to which each of third and fourth rotor assemblies 605-1 , 605-2 is subject to.

[0080] The many features and advantages of the present disclosure are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the present disclosure that fall within the true spirit and scope of the disclosure. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the present disclosure to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the present disclosure.

[0081] Moreover, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be used as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present disclosure. Accordingly, the claims are not to be considered as limited by the foregoing description

Claims

WHAT IS CLAIMED IS:

1. A rotor assembly comprising: a first rotor mounted on a first drive shaft; a second rotor mounted on a second drive shaft that is concentrically mounted on the first drive shaft; a first motor operatively connected to the first rotor, the first motor configured to rotate the first rotor in a first direction; a second motor operatively connected to the second rotor, the second motor configured to rotate the second rotor in a second direction; and a controller configured to operate the first and second motors independently, wherein the controller operates the first motor and the second motor independently to control a blade crossing azimuth based on an angle of inflow.

2. The rotor assembly of claim 1 , wherein each of the first rotor and second rotors includes a two-bladed rotor.

3. The rotor assembly of claim 1 , further comprising: a first sensor configured to detect a position of the first rotor; and a second sensor configured to detect a position of the second rotor.

4. The rotor assembly of claim 1 , further comprising: a first sensor configured to detect a speed of the first motor; and a second sensor configured to detect a speed of the second motor.

5. The rotor assembly of claim 1 , further comprising: a bearing disposed between the first drive shaft and the second drive shaft, and wherein the bearing includes a first bearing and a second bearing located concentrically between the first drive shaft and the second drive shaft.

6. The rotor assembly of claim 5, wherein the second motor is positioned along a longitudinal axis of the rotor assembly between the first bearing and the second bearing.

7. The rotor assembly of claim 1 , wherein a hub of the first rotor is mounted to a distal end of the first drive shaft relative to an engagement between the first drive shaft and a bearing.

8. The rotor assembly of claim 1 , wherein a hub of the second rotor is mounted to a distal end of the second drive shaft relative to an engagement between the second drive shaft and a bearing.

9. The rotor assembly of claim 1 , wherein the first motor is attached to the first drive shaft between the first rotor and the second rotor along a longitudinal axis of the rotor assembly.

10. The rotor assembly of claim 9, wherein the second motor is attached to the second drive shaft between the first rotor and the second rotor along the longitudinal axis of the rotor assembly.

11. An air mobility vehicle (“AMV”) comprising: a fuselage; a first wing attached to the fuselage; a second wing attached to the fuselage; a first rotor assembly and a second rotor assembly attached to the first wing; a third rotor assembly and a fourth rotator assembly attached to the second wing; at least one lift rotor assembly attached to at least one of the first wing and the fuselage; and a controller configured to operate the at least one lift rotor assembly, wherein the at least one lift rotor assembly includes: a first rotor mounted on a first drive shaft, a second rotor mounted on a second drive shaft that is concentrically mounted on the first drive shaft, a bearing disposed between the first drive shaft and the second drive shaft, a first motor operatively connected to the first rotor, the first motor configured to rotate the first rotor in a first direction, a second motor operatively connected to the second rotor, the second motor configured to rotate the second rotor in a second direction, and wherein the controller operates the first motor and the second motor independently to control a respective blade crossing azimuth.

12. The air mobility vehicle of claim 11 , wherein each of the first rotor and the second rotor includes a two-bladed rotor.

13. The air mobility vehicle of claim 11 , wherein the at least one lift rotor assembly includes a first lift rotor assembly and a second lift rotor assembly, and wherein the controller operates the first and second motors for the first lift rotor assembly independently of the first and second motors of the second lift rotor assembly to control a blade crossing azimuth for each of the first and second lift rotor assemblies.

14. The air mobility vehicle of claim 13, wherein the controller operates the first and second motors for the first lift rotor assembly to provide a first blade crossing azimuth that is normal to an angle of respective inflow for the first lift rotor assembly.

15. The air mobility vehicle of claim 14, wherein the controller operates the first and second motors for the second lift rotor assembly to provide a second blade crossing azimuth that is normal to an angle of respective inflow for the second lift rotor assembly.

16. The air mobility vehicle of claim 11 , wherein the at least one lift rotor assembly comprises: a first sensor configured to detect a position of a respective first rotor; and a second sensor configured to detect a position of a respective second rotor.

17. The air mobility vehicle of claim 11 , wherein the at least one lift rotor assembly comprises: a first sensor configured to detect a speed of a respective first motor; and a second sensor configured to detect a speed of a respective second motor.

18. A method of controlling a blade-crossing azimuth for rotors of a counter-rotating rotor assembly, the method comprising: receiving system monitored parameter information and determining inflow parameter values; determining a required blade crossing azimuth based on the inflow parameter values; accessing rotor speeds for the rotors and determining an operational blade crossing azimuth; determining a speed deviation for each of the rotors based on an azimuth deviation between the required blade crossing azimuth and the operational blade crossing azimuth; and controlling a motor for each of the rotors based on a respective speed deviation.

19. The method of claim 18, further comprising: monitoring the rotors for realization of the required blade crossing azimuth; and determining an absolute speed deviation between the rotor speeds.

20. The method of claim 18, further comprising logging values of operating parameters at a time of the realization including an amount of time between a determination of the required blade crossing azimuth and the realization.

21 . A system for controlling a blade-crossing azimuth for rotors of a counter-rotating multi-rotor assembly, the system comprising: a rotor assembly including rotors and motors that drive the rotors; one or more processors; and one or more computer readable media comprising instructions which, when executed by the one or more processors, cause the one or more processors to perform operations, the operations comprising: receiving system monitored parameter information and determining inflow parameter values; determining a required blade crossing azimuth based on the inflow parameter values; accessing rotor speeds for the rotors and determining an operational blade crossing azimuth; determining a speed deviation for each of the rotors based on an azimuth deviation between the required blade crossing azimuth and the operational blade crossing azimuth; and controlling a motor for each of the rotors based on a respective speed deviation.

22. The system of claim 21 , further comprising: monitoring the rotors for realization of required blade crossing azimuth; and determining an absolute speed deviation between the rotor speeds.

23. The system of claim 21 , further comprising logging values of operating parameters at a time of the realization including an amount of time between determining the blade crossing azimuth and the realization.